The ability to produce per-hydroxylated icosahedral boron compounds opens up a new field of boron cluster chemistry where the aromatic icosahedral cluster functions as the scaffolding for reactions performed on its oxygen sheathing. For example, Cs2[closo-B12(OH)12] can be used as the central core for the formation of dodeca-substituted monodisperse organic and inorganic compounds known as closomers, which are distinguished from dendrimers. The spacing of the per-hydroxylated icosahedral boron is reflected in the closomer species derived from it by simple organic reactions, which are characteristic for the hydroxyl group including carboxylate ester and alkyl ether formation. The resulting closomers may have spaced radial substituents of chosen size, hydrophilicity, ionic charge. Thus, the closomers display functions derived from their collected passenger molecules. Applications of these compounds may involve the development of chemical strategies making possible the synthesis of clusters in which the vertices become the anchoring site for a predetermined function. Such functions include, but are not limited to, tumor cell targeting moieties, gadolinium chelators from MRI contrast agents, plasma membrane penetrators, radionuclide chelators for diagnosis or therapy, fluorophores, chemotherapeutics, targeting and therapeutic peptides, carbohydrates and glycobiologics, synthetic antigens, RNA and DNA segments, immunoproteins, etc.
Current synthetic pathways to per-hydroxylated icosahedral boron compounds employ acid-catalyzed hydroxylation of icosahedral boron compound requiring the use of an H2O2 oxidant. However, the H2O2 oxidant poses increased risk of explosive oxidation of the B122− cage. Risk of explosive oxidation makes scaling reactions to a higher volume particularly unattractive.
Therefore, there is a need for improved synthetic routes to per-hydroxylated icosahedral boron compounds.